(1) Field of the Invention
The present invention relates to a liquid crystal display device, and in particular, to a liquid crystal display device where the outer shape in a plane of the backlight for illuminating the liquid crystal display panel has at least one corner of which the angle is greater than 90°.
(2) Description of the Related Art
Though conventional liquid crystal display devices generally use a liquid crystal display panel in rectangular form, liquid crystal display devices in irregular form, where the outer shape of the liquid crystal display panel in a plane has an angle that is not 90°, have recently been demanded for large-scale monitors, display devices for amusement, display devices for industrial machinery and liquid crystal display devices mounted in cars.
WO 2008/062575A1 is a prior art document showing an example of a liquid crystal display device in irregular form. In such a liquid crystal display device in irregular form, the backlight for illuminating the liquid crystal display panel is also not rectangular so as to match the form of the liquid crystal display panel. There are also cases where the backlight is not rectangular even if the liquid crystal display panel is rectangular.
When the backlight is not rectangular, particularly when the outer shape of the backlight in a plane has a corner of which the angle is greater than 90°, as shown in FIG. 1, the light guide plate LG also has a corner A of which the angle θ is greater than 90° so as to match the outer shape of the backlight, and in addition, light emitting diodes LED are aligned along the two sides (s1, s2) that form the corner. In this structure, the regions B and C, shown by the dotted lines, become regions of low brightness.
This is because, as shown in FIG. 2, which is a diagram showing an enlargement of the portion in the vicinity of the corner A in FIG. 1, light emitting diodes LED are aligned along the outer shape of the light guide plate LG where the main components M1 and M2 of the light for illumination emitted from the light emitting diodes LED are in such a direction as to progress perpendicularly to the sides (s1 and s2) of the light guide plate LG in the structure.
Because the light for illumination emitted from the light emitting diodes LED slightly radiates and the form on the sides of the light guide plate LG through which the light enters makes the light spread, the light for illumination that has entered into the light guide plate LG tends to spread and radiate as shown in FIG. 2, and in particular, the main component of the light for illumination propagates in the directions perpendicular to the sides (s1 and s2).
Therefore, as shown in FIG. 1, the light for illumination from the light emitting diodes aligned along the upper side s1 propagates in the downward direction in the diagram (L2 to L4), while the light for illumination from the light emitting diodes aligned along the side s2 propagates through the light guide plate LG in the diagonally inward direction (L1 and L5). As a result, most of the light for illumination is directed towards the center portion of the screen inside the light guide plate LG, and thus, the corner portions of the screen, particularly the dotted line regions B and C, receive a small amount of light for illumination, thereby becoming regions of low brightness.